Added a unit test.

Author: chhsia0

Diff for: Gopkg.lock

@@ -0,0 +1,18 @@
+package main
+
+import (
+	"github.com/google/go-containerregistry/pkg/v1"
+)
+
+// GetDigest returns the digest of an OCI image index. If there is only one image in the index, the
+// digest of the image is returned; otherwise, the digest of the whole index is returned.
+func GetDigest(ii v1.ImageIndex) (v1.Hash, error) {
+	im, err := ii.IndexManifest()
+	if err != nil {
+		return v1.Hash{}, err
+	}
+	if len(im.Manifests) == 1 {
+		return im.Manifests[0].Digest, nil
+	}
+	return ii.Digest()
+}

Diff for: cmd/imagedigestexporter/digest.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/empty"
+	"github.com/google/go-containerregistry/pkg/v1/random"
+)
+
+func TestGetDigest(t *testing.T) {
+	mustGetIndex := func(ii v1.ImageIndex, err error) v1.ImageIndex {
+		if err != nil {
+			t.Fatalf("must get image: %s", err)
+		}
+		return ii
+	}
+	mustGetManifest := func(im *v1.IndexManifest, err error) *v1.IndexManifest {
+		if err != nil {
+			t.Fatalf("must get manifest: %s", err)
+		}
+		return im
+	}
+	mustGetDigest := func(h v1.Hash, err error) v1.Hash {
+		if err != nil {
+			t.Fatalf("must get digest: %s", err)
+		}
+		return h
+	}
+	indexSingleImage := mustGetIndex(random.Index(1024, 4, 1))
+	indexMultipleImages := mustGetIndex(random.Index(1024, 4, 4))
+	tests := []struct {
+		name     string
+		index    v1.ImageIndex
+		expected v1.Hash
+	}{
+		{
+			name:     "empty index",
+			index:    empty.Index,
+			expected: mustGetDigest(empty.Index.Digest()),
+		},
+		{
+			name:     "index with single image",
+			index:    indexSingleImage,
+			expected: mustGetManifest(indexSingleImage.IndexManifest()).Manifests[0].Digest,
+		},
+		{
+			name:     "index with multiple images",
+			index:    indexMultipleImages,
+			expected: mustGetDigest(indexMultipleImages.Digest()),
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			digest, err := GetDigest(test.index)
+			if err != nil {
+				t.Fatalf("cannot get digest: %s", err)
+			}
+			if diff := cmp.Diff(digest, test.expected); diff != "" {
+				t.Errorf("get digest: -want +got: %s", diff)
+			}
+		})
+	}
+}

Diff for: cmd/imagedigestexporter/digest_test.go

@@ -22,7 +22,6 @@ import (
 	"log"
 	"os"
 
-	"github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/layout"
 	v1alpha1 "github.com/tektoncd/pipeline/pkg/apis/pipeline/v1alpha1"
 )
@@ -56,17 +55,7 @@ func main() {
 			log.Printf("ImageResource %s doesn't have an index.json file: %s", imageResource.Name, err)
 			continue
 		}
-		// If there is only one image in the index, report the digest of the image; otherwise, report the digest of the whole index.
-		digest, err := func() (v1.Hash, error) {
-			im, err := ii.IndexManifest()
-			if err != nil {
-				return v1.Hash{}, err
-			}
-			if len(im.Manifests) == 1 {
-				return im.Manifests[0].Digest, nil
-			}
-			return ii.Digest()
-		}()
+		digest, err := GetDigest(ii)
 		if err != nil {
 			log.Fatalf("Unexpected error getting image digest for %s: %v", imageResource.Name, err)
 		}